(RFE/RL) -- In a new 26-page report, Human Rights Watch (HRW) says Hamas, the Islamist movement that controls Gaza, used the recent conflict with Israel as a cover for a series of brutal attacks against its own citizens -- Palestinians who are the political opponents of Hamas.

The U.S.-based nongovernmental organization says Hamas continued to carry out killings, abductions, and torture of its political opponents in Gaza after the Israelis ended their 22-day offensive there.

"Hamas took advantage of the chaos and went after its opponents. It cleaned house," says Fred Abrahams, a researcher for HRW who worked on the report.

"They went after people suspected of collaboration with Israel, but also its political opponents -- even people who were just criticizing Hamas. So it was a very brutal internal crackdown that came under the cover of the Israel-Hamas conflict."

HRW says 18 Palestinians were killed by gunmen linked to Hamas during the three-week war, and 14 others were killed afterward. Abrahams describes details of Hamas's tactics and abuses as disconcerting.

"Hamas targeted especially members of Fatah -- its chief rival [political faction], and members of the Fatah security forces. It detained them, beat them, tortured them -- in some cases leading to deaths," Abrahams says.'Kneecapping' Critics

"A particular tactic that Hamas used during the Israeli campaign was 'kneecapping,' or shooting in the leg," he adds. "There were 49 such cases documented by local human rights groups -- mostly Fatah members and supporters."

But the HRW report doesn't rely solely on the testimony of local human rights advocates in Gaza. Abrahams describes one kneecapping victim in Egypt who "made it out of Gaza for medical care. He is sitting in a wheelchair and he was shot because he welcomed the Israeli attacks."

"One man, however, told us he was on the street speaking critically of Hamas and someone overheard what he was saying. And that night, 12 men came to his home, dragged him outside, took him around the corner and shot him repeatedly in both legs," Abrahams says. "He was not even a Fatah member. He was simply someone who objected to the policies of Hamas."

Abrahams concludes that Hamas's brutal actions against Palestinian civilians in Gaza makes a "mockery" of its claims that it is trying to bring law and order to the area.

"And it is double suffering for the Gaza citizens. On top of Israel's massive offensive, which has destroyed so many lives, on top of that there is now an abusive local authority, Hamas, which is abducting people, torture, killings, and detentions," Abrahams says. "The Gazans are getting it from both sides."

Meanwhile, although HRW says violations in Gaza have lessened in recent weeks, the rights group warns that Hamas authorities are still failing to address seriously the crimes by its security forces during and after the Israeli offensive.

In a previous report, HRW criticized Israel for its actions during the offensive, in which more than 1,000 Palestinians were killed, including hundreds of women and children.

HRW has documented the use by Israeli forces of using highly flammable white phosphorous in densely populated neighborhoods, and said the actions constituted "evidence of war crimes." Thirteen Israelis died during the campaign.